1. Field of the Invention
The present invention is concerned with optical materials and optical elements using the same.
2. Description of the Related Art
Techniques have been known which can control light or develop color by using polymer gel materials to control light transmittance and light scattering property; in the techniques, the polymer gel materials are stimulus-responsive polymer gels which reversibly change their volumes (swell and contract) when provided with stimuli such as pH change, ionic strength change, adsorption and desorption of chemical substances, change in solvent composition, application of heat, application of light, and application of electric stimuli.
The following techniques have been known as techniques for controlling light transmittance and light scattering property without using colorants. Elements are proposed in Japanese Patent Application Laid-Open (JP-A) Nos. 61-151621 and 62-925. The elements each control light scattering by changing the difference in refractive index between the solvent and a polymer gel. When the temperature is changed, the polymer gel absorbs or releases liquid, so that the polymer gel swells or contracts in accordance with the temperature change. The elements can control light scattering by utilizing the change in refractive index of the polymer gel accompanying the swelling or contraction of the polymer gel. Therefore, the elements can display images.
Other elements have been proposed (for example in JP-A No. 4-134325) which display images utilizing the change in light scattering property of a polymer gel upon swelling or contraction of the polymer gel caused by an electric stimulus. Further, elements have been proposed (for example in Japanese Patent Publication (JP-B) No. 7-95172) which display images utilizing the change in light scattering property of a polymer gel; the light scattering property changes when a conductive polymer in the polymer gel is doped or undoped with ions to change the pH. Moreover, elements are disclosed (for example in JP-A No. 5-188354) which display images formed by transparent areas and opaque areas; the elements each use a polymer gel which absorbs or releases liquid according to change in electric field to swell or contract, the elements utilize the swelling and contraction of the polymer gel so that the elements can shield light, reflect light, scatter light or control light transmittance, thereby displaying images.
The following techniques have been known which can control color developing property using colorants. Light controlling elements are disclosed (for example in JP-A No. 61-149926) which each comprise a combination of a colored liquid containing a pigment dispersed therein and a polymer gel which absorbs or releases liquid according to change in electric field; in the elements, the shape of the polymer gel changes to move the colored liquid, thereby displaying images. Elements are disclosed (for example in JP-A Nos. 61-151625 and 62-927) which use a colored polymer gel; in the elements, the optical density decreases when the polymer gel swells and the optical density increases when the polymer gel contracts. Elements are disclosed (for example in JP-A No. 4-274480) which uses a polymer gel bound to a colorant; in the elements, the optical density is changed by a change in the volume of the polymer gel, thereby displaying images. Further, elements are disclosed (for example in JP-A No. 9-160081) whose hues are changed by a change in the volume of a polymer gel on which pigment particles or colored particles are adsorbed; in the elements, white color is displayed when the polymer gel swells and the color of the pigment particles or the colored particles is displayed when the polymer gel contracts, thereby displaying images.
The inventors of the present invention proposed novel color developing materials which are excellent in contrast (for example in Japanese Patent No. 03543641). The color developing materials each include a composition containing a polymer gel and a pigment. The polymer gel is a polymer gel which can swell or contract by absorbing or releasing liquid when a stimulus is applied. The pigment is contained in the polymer gel and the concentration of the pigment is not lower than the saturated absorption concentration. When the polymer gel contracts, the pigment aggregates locally to decrease the light absorption efficiency, so that the composition has a high light transmittance. When the polymer gel swells, the pigment diffuses in the entire composition to increase the light absorption efficiency, so that the composition develops color.
Conventional light controlling techniques and color developing techniques using polymer gels have used water, water-based liquids, and highly volatile organic solvents as the liquids to be absorbed or released by the polymer gel. Therefore, it has been necessary to prevent evaporation of the liquids by sealing the polymer gels and the liquids in cells formed by glass substrates and the like. When the substrates are resin films, the resin films have to have a high gas-blocking property, so that the costs of the substrates increase. Further, it has been quite difficult to prevent evaporation of the liquids for a long time even when the liquids are sealed in such cells.